I'm working on a project where I want/have to use a 2S Li-Ion battery-pack. I want my design to be as safe as possible, which is I why I want to use a battery-pack that is protected by an internal BMS.

Most ressources state that balancing is absolutely necessary when using a 2S-configuration. Why is it that I can't find any 2S battery packs with an internal BMS that include a balancing-lead? Most packs have 2, some have 3 leads and include an NTC (which I plan on using anyway). One could guess that the BMS itself does the balancing but this isn't actually stated anywhere. I have checked out some of the protection modules (e.g. PCB-2S20W LI-2S)that are used in the battery-packs advertised on e.g. batteryspace and those include a "COM" connection that connects the mid-point of both cells to the BMS. Does such a mid-point indicate a cell-balancing function or does this serve a different purpose?

My project does not deal with crazy discharge rates (3-4A for short periods max, about 1-1.5 A continuous drain) but actually choosing the right and "safe" battery-pack does not seem to be that trivial.

What is the right way to go about the balancing topic and am I right in assuming that there are indeed BMS-boards that balance the cells on their own?

  • 1
    \$\begingroup\$ "Does such a mid-point indicate a cell-balancing function" - not necessarily, it may be just to shut the whole pack off if the voltage of one cell gets too low even if the other is still ok. \$\endgroup\$
    – Finbarr
    Dec 15, 2022 at 16:20
  • \$\begingroup\$ Thank you for your answer. In the meantime I have contacted a distributor of cells/battery-packs which informed me that balancing just isn't seen as critical/neccessary for low-discharge packs or those with less than 4 series cells. Furthermore the datasheets of the protection ICs used in e.g. the PCB-2S20W PCM indicate that the mid-point is indeed being used to monitor the cell-voltage to shut the pack off, just as you explained. \$\endgroup\$
    – L. T.
    Dec 16, 2022 at 8:57

1 Answer 1


As mentioned in the comment above and in reference to what the engineers at batteryspace told me: Balancing is not seen as a critical feature on low-discharge Li-Ion packs or such packs that have less than 4 cells in series.

While there is a "COM" or "MID" connection on most protection modules, this may not be a direct indicator of a balancing function and could instead be used to monitor the individual cell-voltages as seen on e.g. the PCB-2S20W LI-2S module.

There are however some protection modules like the PCM-S2A5B that do offer a balance function, which is explicitly mentioned in the datasheet.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.